A technical guide to district heating Robin Wiltshire, Jonathan Williams and Paul Woods A technical guide to district heating Robin Wiltshire and Jonathan Williams (BRE) Paul Woods (AECOM) ii The research and writing for this publication has been funded Any third-party URLs are given for information and reference by BRE Trust, the largest UK charity dedicated specifically to purposes only and BRE Trust and IHS do not control or warrant research and education in the built environment. 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Bottom right: Combined heat and power engine in the energy centre at the King’s Cross Central Development (image courtesy FB 72 of Vital Energi) First published 2014 Back cover image Pipe system installed in Sheffield District Heating Network ISBN 978-1-84806-193-4 (image courtesy of Vital Energi) Contents iii Contents Preface iv 1 Introduction 1 2 What is district heating? 2 2.1 Who has implemented schemes in the UK? 2 2.2 Where have schemes been implemented in the UK? 2 2.3 Benefits of district heating 5 2.4 The starting point 6 3 System design 9 3.1 System configuration 9 3.2 Optimisation of system temperatures 13 3.3 Optimisation of system pressures 15 3.4 Designing for flexible development 16 3.5 Summary of district heating overall system design 17 4 Component design 18 4.1 At the energy centre 18 4.2 Heating distribution network 25 4.3 Connection of buildings to district heating 28 4.4 Metering and charging systems 32 4.5 Circulation pumping and pressurisation 34 4.6 System control and monitoring 37 4.7 District cooling 38 5 Operation and maintenance 39 5.1 Introduction 39 5.2 Record information on completion of construction 39 5.3 Planned preventative maintenance 39 5.4 Surveillance systems for preinsulated pipe systems 40 5.5 Water treatment 41 6 References 45 7 Relevant standards, codes of practice and publications 46 7.1 National Standards 46 7.2 IEA publications 47 7.3 Other guides and publications 48 iv A technical guide to district heating Preface The fundamental idea of district heating (DH) is a pipe network The efficient use of energy together with the use of surplus and that allows centralised heat sources to be connected to many renewable sources means using DH networks can significantly heat consumers. Typically a DH network comprises three main reduce emissions of carbon dioxide. Integration of these sources components: one or more energy centre(s); the pipe network of available waste heat means that DH produces significantly itself; and connections to the heat customers. In this way the lower emissions of greenhouse and other gases compared with system presents an overall heat demand that is the aggregate alternatives. It is also much easier to make sure emission targets of all the individual consumer requirements. The greater size of are reached with a small number of large producers than a large load leads to an economy of scale and the aggregation means number of small producers. the load is smoother, leading to more efficient and economic operation of plant at the energy centre. It also allows heat to The use of thermal energy from CHP ranges in scale from be provided from sources that cannot readily be used at an large centralised power generation plant to smaller scale units individual building level. implemented as embedded generation. While the former is common in other European countries that have implemented Networks also provide fuel flexibility for the future: new low- large town and citywide DH networks, it is the smaller plant, carbon and renewable sources can be integrated as soon as they usually reciprocating engines, that is predominant in the UK. become available and the network quickly provides an easy way Such units are commonly the initial building block around which to convert a large number of customers to these new sources. new networks can grow. The benefits of DH have led to a great deal of interest in the Making use of surplus energy or integrating renewable sources technology, and speculation and estimates of its future growth. can increase energy security. Fuel supply reliability and flexibility Initial results from the heat networks model being developed by is enhanced by using indigenous fuels like biomass or waste. the Department of Energy and Climate Change (DECC) suggest Power grid reliability is strengthened by generating power that up to 20% of UK domestic demand might be served by nearer to population centres, and with CHP local demands can heat networks by 2030, with other UK-based studies indicating often still be met even when the main grid supply is interrupted 14–20% of current heat demand could be met in this way. The if the CHP plant is configured to allow operation in island mode. European Heat Road Map study estimates that about 50% of the heat demand across Europe in 2050 could potentially be DH networks are potentially able to make use of heat from served by DH, thereby opening up opportunities for extended any source. In this way thermal networks can be supplied by use of sustainable and renewable energy sources for heating low-carbon or zero-carbon sources, or new technologies, or purposes at relatively low costs. waste heat sources that become available. This also means that thermal grids, once established, are able to progressively It is important that networks are designed carefully based decarbonise. on sound engineering principles with particular importance attached to securing a low return temperature for efficient From the perspective of building owners and managers, operation. This guide provides technical information on DH, modern DH offers economic and technical benefits. It reduces divided into sections on system design, component design, and operating, maintenance and capital costs associated with boilers operation and maintenance, with a comprehensive information in individual buildings, while the consumer receives energy and reference section. services that the DH producer provides in the most efficient way possible. The main driver making the business case for DH is the use of thermal energy that will otherwise be wasted. In particular, DH When developed at scale, DH networks also provide allows the efficient use of thermal energy from combined heat competition between different heat sources and fuels and can and power (CHP) plants, refuse incineration plants, waste heat therefore be an important element in liberalised energy markets. from industrial processes, natural geothermal heat sources and In large-scale integrated DH systems, all available heat sources fuels that are more easily used centrally including renewables can compete to the benefit of the consumers who are united as like wood waste and residues. a bulk buyer. 1 Introduction 1 1 Introduction This guide concerns the technical aspects of district heating • ‘System design’ describes the DH network as a whole; it is (DH) networks.